@TDHarris52 If you explain something to someone and he does not understand you, try again and explain it in another way. Just pointing them to the part they didn’t understand in the first place does not help.
As I understand it you add music that’s on your PC to a Sonos device via the PC app. The Sonos system will then remeber the path to the music on the Sonos device and show it to you via the app on your PC or phone. It’s the same with playlists: as I understand it, if they are on your computer in the music you can add them to Sonos (I do not use this feature myself). And playlists made with Sonos are also stored on the Sonos devices and only shown to you in the app. So removing and reinstalling the app will not change playlists.
The process you are describing look more liking the process Sonos calls adding to a queue. This way you add songs to a queue/list stored on a device, but the queue is not meant to be saved. Restarting the Sonos device wil wipe the queue. You can make playlists in the Sonos app (take a look here - scroll down a little: https://www.pocket-lint.com/speakers/news/sonos/139397-sonos-tips-and-tricks-get-the-most-out-of-your-multi-room-speaker-system). The app will store them on the Sonos devices.
Playlists stored on a Sonos device cannot be saved to a PC as far as I know.